Process for the manufacture of oxygencontaining derivatives of olefins in an electrochemical cell



APYII 1968 J. A. M. LEDUC 3,379,

PROCESS FOR THE MANUFACTURE OF OXYGEN-CONTAINING DERIVATIVES OF OLEFINSIN AN ELECTROCHEMICAL CELL Filed June 21, 1966 4 Sheets-Sheet lINVENTOR. Joseph fldrim AZ lm'zlc ATTORNEYS Apnl 23, 1968 J. A. M. LEDUC3,379,627

PROCESS FOR THE MANUFACTURE OF OXYGEN-CONTAINING DERIVATIVES OF OLEFINSIN AN ELECTROCHEMICAL CELL Filed June 21, 1966 4 Sheets-Sheet 2INVENTOR. (T0540)? Adrien M .Zeauc April 23, 1968 Filed June 21,

34 35 g 1 41 I i 42 f Ti: Z k

21 I R A J-A.M.LEDUC 3,379,627 PROCESS FOR THE MANUFACTURE OFOXYGEN-CONTAINING DERIVATIVES OF OLEFINS IN AN ELECTROCHEMICAL CELL 4Sheets-Sheet 5 INVENTOR Jamal; Adrien AZ Zewz/c BY 90 w 2 9 April 23,1968 J. A. M. LEDUC PROCESS FOR THE MANUFACTURE OF OXYGEN-CONTAININGDERIVATIVES OF OLEFINS IN AN ELECTROCHEMICAL CELL 4 Sheets-Sheet 4 FiledJune 21, 1966 INVENTOR. Jasepfi Adrien AZ Zea ac A TTORNEKS UnitedStates Patent 3,379,627 PROCESS FOR THE MANUFACTURE OF OXYGEN-CONTAINING DERIVATIVES 0F OLEFINS IN AN ELECTROCHEMICAL CELL EoscphAdrien M. Leduc, Short Hills, N.J., assignor to Pullman incorporated,Chicago, Ill., a corporation of Delaware Continuation-impart ofapplication Ser. No. 299,519, Aug. 2, 1963, which is acontinuation-in-part of application Ser. No. 244,991, Sept. 20, 1962.This application June 21, 1966, Ser. No. 559,271

9 Claims. (Cl. 20480) This application is a continuation-in-part of myprior and copending applications Ser. No. 224,991, filed Sept. 20, 1962,now Patent No. 3,288,692, and Ser. No. 229,519, filed Aug. 2, 1963,which in turn is a continuation-in-part of said application Ser. No.224,991.

This invention relates to a particular improvement in the manufacture ofoxygen-containing derivatives of olefins in an electrochemical cell andto improved apparatus relating thereto. In one aspect the inventionrelates to an improved method for the manufacture of halohydrin andoxide derivatives of an olefin in an electrochemical cell provided withparticular metallic electrodes. In another aspect the invention relatesto improved apparatus comprising metallic electrodes and to improvedelectrode structures particularly useful as the anodic surface of anelectrochemical cell in which an olefin is reacted in the anodic regionof the cell.

In accordance with my said application Ser. No. 224,991, an improvedmethod is described and claimed for converting an olefin within anelectrochemical cell to the corresponding olefin oxide derivative. Themethod comprises providing a cell containing an aqueous solution of ametal halide, such as an alkali metal halide or an alkaline earth metalhalide, subjecting said aqueous medium to the action of an electrolyzingcurrent, feeding an olefin such as ethylene or propylene to the anodicregion of the cell such that the corresponding halodyrin derivative ofthe olefin is formed, maintaining the flow of aqueous medium from theanodic region towards the cathodic region such that the halohydrin isdehydrohalo genated in the aqueous medium in the vicinity of the cathodeto form olefin oxide which is withdrawn from the cell as the principaloxygen-containing derivative of the olefin. The overall principalreaction which takes place in the aqueous medium in the vicinity of theanode is expressed by the following equation in which MX represents analkali metal halide,

represents the reactive ethylenic point of unsaturation of the olefinreactant, and X is halogen corresponding to the halogen of the metalhalide:

While this halohydrin forming reaction is occurring in the vincity ofthe anode, water of the aqueous electrolyte bath is electrolyzed in thevicinity of the cathode to generate hydrogen and hydroxyl anions whichcause the aqueous medium in the vicinity of the cathode to becomealkaline, according to the following equation:

By maintaining the flow of aqueous medium within the cell from theanodic region towards the cathodic region, the aqueous medium containinghalohydrin i continuously transported to the alkaline medium in thecathodic region wherein the halohydrin is dehydrohalogenated to3,379,627 Patented Apr. 23, 1963 form the corresponding olefin oxidewhich is recovered as the product of the process, this reactionoccurring as follows:

H 0 (3) in which M is alkali metal and X is halogen. In order tofacilitate the discussion of the present invention, the term anolyte asused herein refers to the aqueous electrolyte medium at and in thevicinity of the anode or anodes of the electrolytic cell, i.e., thatportion of the aqueous medium in which the formation of halohydrinoccurs; and the term catholyte refers to the aqueous electrolyte mediumat and in the vicinity of th cathode or cathodes of the electrolyticcell, i.e., that portion of the aqueous medium in which the reactions ofEquations 2 and 3 occur.

In using anodes composed of graphitic carbon, the power requirement ofthe electrochemical cell is relatively high and in addition it is foundthat after prolonged continuous use of the cell, the graphite becomeseroded by olefinic feed resulting in a reduction in the thickness of theanode and widening of the gap between the electrodes thereby causing afurther increase in the potential drop in the electrolyte and in theanode itself. A further disadvantage particularly troublesome when theolefin oxide is produced in a diaphragm cell is that duringdeterioration of the graphite by erosion and by formation of carbonoxides, loose particles of graphite and impregnants usually found ingraphitic carbon electrodes cause plugging of the diaphragm. Due tothese operational drawbacks and disadvantages of the graphitic anodes,the cell is necessarily operated under a gradually increasing powerdemand. This requires interruption of the operation of the cell morefrequently than is otherwise necessary when a gaseous reactant is notfed to the anode, in order to replace the anodes and the cell diaphragm.One approach to solving the problem of frequency of replacement ofgraphitic anodes is to use anodes of a relatively thicker cross-sectionin order to provide an anode of longer life. A major disadvantage ofthis attempt to solve the problem, however, is that a cell of givengeometric dimensions and fioor space can be provided with only a lessernumber of electrodes and thus the product output of the cell isdecreased accordingly. This problem of maximizing product capacity isespecially magnified when the olefin reactant is fed to the innerchamber of a porous hollow blade of graphitic carbon such that theolefin reacts at the olefin-electrolyte-anode interface. This type ofhollow porous anode is necessarily of a relatively wide cross-section inorder to provide adequate mechanical strength but again the productcapacity of a cell of given dimensions is decreased since the cell canbe equipped with only a fewer number of such hollow electrodes. Afurther disadvantage in using graphitic carbon anodes of either thesolid blade or hollow porous blade type in my process is that aby-product is formed which adheres to the graphitic surface such thatthe yield of desired oxygen-containing product decreases with time.

Accordingly, it is an object of this invention to provide an improvementin the manufacture of oxygen-containing derivatives of an olefiniccompound in an electrochemical cell in which an olefinic compound isreacted in the anolyte.

Another related object is to provide an improvement in said method suchthat the voltage drop during operation of the cell is substantiallydecreased.

Another object is to provide an improvement for the manufacture ofoxygen-containing derivatives of an olefin by which a relativelyconstant yield of desired product is obtained during prolongedcontinuous operation of the cell.

Another object of this invention is to provide an improved electrodeparticularly useful in an electrochemical cell in which a gaseousolefinic compound is reacted in the vicinity of that electrode.

Another object is to provide such an electrode which has good mechanicalstrength in the porous state, is not eroded by the olefinic reactant,and is chemically inert to the aqueous reaction medium.

Another object is to provide an electrode of generally increasedlongevity and decreased cross-section for use as the anode of anelectrochemical cell in which an olefin is converted initially to itscorresponding halohydrin derivative in the anolyte.

Another object is to provide an electrode having the above propertiesand which allows for the conversion of an olefin to an oxygen-containingderivative such as halohydrin and oxide derivatives, at a relativelyconstant voltage which is lower than required when a graphite electrodeis utilized.

A further object is to provide an improvement in an electrochemical cellespecially useful for the production of olefin oxides.

A further object is to provide an improved base of an electrochemicalcell which base is anodic and in which cell a gaseous feed is reacted inthe anolyte.

Various other objects and advantages of this invention will becomeapparent to those skilled in the art from the accompanying descriptionand disclosure.

In accordance with one aspect of the present invention an improvedprocess is provided for producing an oxygen-containing derivative of anolefinic compound which comprises subjecting an aqueous medium having ahalide electrolyte dissolved therein and contained in an electrochemicalcell to a direct electric current between an anode and a cathode, theanode comprising at least one metal selected from the group consistingof titanium, tantalum, zirconium and niobium and having at least oneplatinum group metal on the surface thereof, feeding an olefiniccompound to the cell such that it is contacted with anolyte, andwithdrawing from said cell efiiuent containing an oxygen-containingderivative of the olefinic reactant as a product of the process.Depending largely on the control of the direction of how of the aqueousmedium within the cell, the halohydrin derivative of the olefin whichforms in the anolyte may be recovered as the principal oxygen-containingderivative of the olefin or the halohydrin may be dehydrohalogenatedwithin the cell to form the corresponding olefin oxide which isrecovered as the principal oxygen-containing organic prodnot of theprocess.

The term platinum group metal as used herein is intended to include eachof the Group VIII metals having an atomic number of at least 44, namely,platinum, palladium, rhodium, iridium, ruthenium, and osmium, as well asalloys thereof such as alloys of these metals with one another. Forconvenience the following discussion is drawn primarily to a descriptionof the use of platinum as the platinum group metal but it is to beunderstood that any one of the aforesaid platinum group meals issatisfactorily employed in place of or in addition to platinum withoutdeparting from the scope of this invention. The second metalliccomponent of the anodic electrodes described herein, i.e., at least oneof titanium, tantalum, zirconium and niobium, is referred to herein asthe substrate metal by which term is meant any one of these metalseither alone or as an alloy such as alloys of these metals with oneanother. Although the specific discussion of the present invention isprimarily directed to titanium, it is to be understood that the presentteachings are also intended to cover the use of tantalum, zirconium andniobium in place of or in combination with titanium. Also includedwithin the scope of this invention is the use of electrodes comprising athird type of metallic component, referred to herein as the undercoat,positioned between the substrate metal and platinum group metal. Theundercoat may be in the form of: (l) a metallic layer such as a layer ofgold, silver or an alloy such as gold-palladium, silver-lead,lead-bismuth, lead-antimony, chromium-silver, chromium-lead,lead-tellurium and lead-selenium alloys with and without the presence ofa ternary metal such as the aforesaid alloys in further combination withpalladium or rhodium; (2) a binder metal which binds the platinum groupmetal to the substrate metal by diffusion of the binder metal into boththe platinum group metal and substrate; or (3) a porefilling surfacecomprising a metal or alloy having good throwing power such thatrecessed areas on the surface of the substrate are covered with acontinuous non-porous film prior to being coated with the platinum groupmetal.

In the electrochemical manufacture of oxygen-containing derivatives ofolefins by my improved method comprising the use of the aforesaidparticular metallic electrodes as the anodic surface, the powerrequirement of the electrochemical cell is less than when the cell isoperated under comparable conditions using graphitic anodes. Inaddition, the process is operable at a substantially constant appliedcurrent and the voltage drop during continuous operation issubstantially less than when graphitic carbon anodes are employed. It isfurther found that a relatively constant yield of desiredoxygen-containing product is achieved over prolonged periods ofcontinuous operation of the cell provided with the metallic anodicsurface. On the other hand, when the cell is operated using graphiticcarbon anodes, the yield of oxygencontaining product fluctuates andgradually lessens over prolonged periods of continuous operation. Thislatter condition is in part attributable to the fact that carbonelectrodes are susceptible to deterioration by physical erosion causedby the olefin feed and contact with the aqueous electrolyte bath and bychemical attack of the acidic anolyte. In addition, a graphitic anodicsurface also tends to become partially coated with an impurity producedduring continuous operation the exact nature of which however is notfully understood. Achievement of a relatively constant yield duringcontinuous operation using the particular metallic electrodes describedherein may be explained on the basis that the metallic surface remainsintact in the sense that it is not substantially deteriorated by physialerosion, chemical attack and does not tend to become coated with theimpurity formed. Further advantages in carrying out my process using theparticular metallic electrodes described herein are that a cell of givengeometry or volume is capable of producing as much as percent moreproduct than a cell fitted with graphite anodes for reasons which willbe discussed in greater detail hereinbelow, and the cell operates at alower average potential without sacrifice of selectively of the processin producing desired products.

In accordance with another aspect of this invention an improvement isprovided in electrical apparatus comprising the base of anelectrochemical cell having the metallic electrodes of this inventionsecured therein and being further provided with a current distributingplate having tightly fitted thereon a layer of at least one of theaforesaid substrate metals (i.e., titanium, tantalum, zirconium orniobium including alloys thereof), the anodized form of said metalproviding the top, exposed surface of the base, the metallic electrodesbeing in electrical association with the current distributing plate.

In order to facilitate further description and understanding of theteachings of this invention reference is had to FIGURES 1 through 12 ofthe accompanying drawings.

FIGURES l, 2, 3 and 4 are three-dimensional views partially cut away ofparticular structures of the electrodes of this invention.

FIGURE 5 is a longitudinal cross-sectional view of an electrochemicalcell provided with a particular anode assembly in accordance with oneembodiment of the structures of this invention.

FIGURES 6, 7, 8, 9 and 10 are longitudinal crosssectional viewsillustrating further embodiments of the anodes and anode assemblies ofthis invention.

FIGURES 11 and 12 are longitudinal cross-sectional views illustratingthe type of cells in which experiments described herein are carried out.

For the purposes of convenience and clarity and to facilitate thedescription and inspection of the figures of the accompanying drawings,the same reference numerals are used to designate common componentparts, chambers and compartments.

In accordance with the embodiment of the metallic electrodes illustratedby FIGURES 1, 2 and 3, electrodes 2, 4 and 6, respectively, are hollowblades, each comprising inner chamber 11, vertical side walls 12, abase, a top enclosure and an inner support or reinforcement means. Thetop of electrodes 2 and 4 of FIGURES 1 and 2, respectively, are shown asflat members designated by numeral 13, these electrodes differing withrespect to the base and inner support means. Thus base 14 of electrode 2of FIGURE 1 is a straight vertical member whereas base 16 of electrode 4of FIGURE 2 is L-shaped. The inner support means of electrode 2 is inthe form of corrugated strips 17 and that of electrode 4 is in the formof resilient screen 18. Electrode 6 of FIGURE 3 differs in that the topenclosure of inner chamber 11 is cylindrical member 21 which may be arod or tube and the inner support means is also a cylindrical member,designated by numeral 22, and is provided with at least one opening 23therethrough. Each of the inner support means of the electrodes ofFIGURES 1, 2 and 3 is held in place by tack or spot welding, and ispreferably composed of a metal which has a relatively low electricalresistance such as stainless steel, copper or one of the aforesaidsubstrate metals such as titanium. With further reference to FIG- URE 3,it is noted that base 19 of electrode 6 is of narrower dimension thanside walls 12 whereas base 14 of electrode 2 of FIGURE 1 is ofsubstantially the same width as side walls 12. The choice of basedepends largely on the width of side walls 12 and when sufiicientlythick such as from 10 to 60 mils, the base may be of such thinnerdimension as shown by FIGURE 3 and still be sulficiently strong towithstand the weight of side walls 12.

Vertical side walls 12 of electrodes 2, 4 and 6 are porous and comprisethe substrate metal having a layer of the platinum group metal on theexterior surface thereof as well as on the interior surface or surfacecreated by the pores of the substrate. The base and top of theelectrodes do not face an opposing electrode surface when assembled inthe operating electrochemical cell and, although they may be platinized,these portions of the electrode need not be and for economic, practicalreasons are usually not platinized. Thus base 14, 16 and 19 ofelectrodes 2, 4 and 6, respectively, and top members 13 and 21 areusually formed of the substrate metal such as titanium and may be ineither porous or non-porous form. However, in order to avoid diffusionof the reactant with which the electrode is contacted through a surfacewhich does not face an opposing electrode surface, the base and topmembers of electrodes 2, 4 and 6 are preferably fluid impervious whichstate is accomplished either by coating the outer surface, when porous,with a paint such as polytetratluoroethylene paint, an epoxy resin,molten polymers such as polyethylene, polypropylene, etc., or by formingthese portions of the electrode of nonporous metal as shown.

Electrode 8 of FIGURE 4 illustrates a self-supporting electrode in theform of a series of contiguous tubes 26 each of which encloses chamber27. Base 28 of electrode 8, as shown, is similar to that of the base ofelectrodes 2 and 6 of FIGURES 1 and 3 in that it is a straight verticalmember and may be of the same thickness as the walls of tubes 26 or ofthinner dimension (as shown),

although it is to be understood that the base may also be L-shapedsimilar to base 16 of electrode 4 of FIGURE 2. Since top enclosure 29 ofelectrod 8 and base 28 also do not face an opposing electrode surface inthe operating electrochemical cell, they need not be platinized and arepreferably formed of the substrate metal in either fluid permeable ornon-porous form as described above in connection with the correspondingportions of electrodes 2, 4 and 6.

As stated above, the electrodes of this invention are especiallysuitable as the anodes of an electrochemical cell in which a fluidreactant such as an olefinic compound is contacted with the anodicsurface. FIGURE 5 to which reference is now had, illustrates anelectrochemical cell provided with the particular electrode 2 ofFIGURE 1. As shown, the cell of FIGURE 5 comprises lower section 5 inwhich a plurality of the electrodes of this invention are secured,middle section 10 which comprises the opposing electrode surface, anduppensection 15 comprising the cover of the cell. These three units areseparable and integral units and are mounted one above the other.Section 5 which is theanode assembly comprises inlet 31, chamber 32,lower base plate 33, and an upper section 34 comprising lower currentdistributing means shown as plate 35 having metallic layer 36 thereon.Current distributing plate 35 is provided with slots 37 and the lowersurface forms the top enclosure of chamber 32. Current distributingplate 35 is formed of an electrolytic grade metal, usually copper, andextends beyond one side of the base such that the extended portion 38serves as the anode terminal to which anode bus connecting plate 46 isconnected. Tightly fitted to current distributing plate 35 such as bycladding, is metallic layer 36 formed of at least one of the aforesaidsubstrate metals (i.e., titanium, zirconium, tantalum, niobium andalloys thereof). Metallic layer 36 is also slotted, the slots thereinbeing aligned with those in current distributing plate 35. As shown byFIGURE 5, base 14 of electrode 2 which is the same as that illustratedby FIG- URE 1, is fitted within the aligned slots of currentdistributing plate 35 and substrate metal layer 36 and is held securelyin place by welding, the weld also providing a fluid tight seal. Baseplate 33 forms the lower enclosure of chamber 32 and is a rigid solidwhich may or may not be electrically conductive and is usually formed ofa ferrous metal such as steel. Side enclosure 39 of chamber 32 may be ofa variety of shapes such as S or Z-shaped as shown, U-shaped, I-shaped,etc., such that it is readily secured to connecting plate 41 of uppersection 34 of the base and to base plate 33. Although side enclosure 39is shown provided with at least one inlet 31, it is to be understoodthat one or more inlets may be positioned within base plate 33 insteadof or in addition to inlet 31. A fluid tight seal is provided betweenside enclosure 39 and upper section 34 of the base by any suitable meanssuch as gasket 42. In view of the fact that chamber 32 is an openchamber additional support is provided by reinforcement brackets 43having slots 44 therethrough.

In utilizing the electrode assemblies of this invention as the base ofan assembled cell, the electrodes extend upwardly therefrom into themiddle section of the cell comprising the opposing electrode su rface.In carrying out my process utilizing the metallic electrodes of thisinvention as the anodic surface, the anode assembly such as thatdesignated by numeral 5 of FIGURE 5 may be used in combination with anysuitable cathodic middle section. When it is desired to convert theolefinic reactant to olefin oxide within the cell, it is especiallydesirable to operate the process in a diaphragm cell in which thecathodic surface is in association with a liquid permeable diaphragmthrough which the anolyte containing the halohydrin derivative of theolefin is passed into the alkaline catholyte wherein the halohydrin isdehydrohalogenated to the olefin oxide which is recovered from the cell.One type of cathodic section with which the particular anode assembliesof this invention may be used is that described and claimed in myaforesaid copending application Ser. No. 299,519 filed Aug. 2, 1963, andwhich is illustrated as section 10 of FIGURE herein. As described in thelatter application, the cathodic surface is foraminous such as in theform of a screen, as shown, and comprises tubular screen 1412. oftubular cathodes 80 having inner support means 119, and vertical screen101 of half cathodes 79 which are the end electrodes. The inner cellchamber within which the electrodes are positioned and to which theaqueous medium is fed such that it flows between the porous metallicsurface of anodes 2 and the foraminous cathodic surface, is defined byvertical walls 101 of each of the two half cathodes 79 and by opposingvertical side walls 82 of which there are two. Each of side walls 82 arealso foraminous and are perpendicular to extend between the two endvertical walls 101. Tubular cathodes 80 which enclose cathodecompartments 85, and half cathodes 79, extend across the full width ofthe inner cell chamber between the opposing side walls 82 and areconnected thereto by welding or by the removable means described andclaimed in my aforesaid application Ser. No. 299,519, such that acontinuous forarninous cathodic surface is provided within middle section of the cell. Thus, by this arrangement, electrodes 2 in functioningas the anodes are in opposed, spaced relationship on each of their fourvertical sides to a foraminous cathodic surface such that the reactiveanodic surface is maximized.

The outer wall of middle unit 19 of the assembled cell of FIGURE 5 iscasing 83 having current distributing means 84 in contact with the outersurface and has upper and lower flanges 87 and 88, respectively, aboutthe edges thereof. Enclosed between casing 83 and the walls of the innercell chamber is a peripheral chamber which, as shown, is divided intotwo compartments, namely, outer compartment 91 and inner compartment 92separated by vertical wall 93 having openings 94 therethrough. The topand bottom enclosures of outer compartment 91 is defined by upper andlower flanges 87 and 88, respectively. The top enclosure of innerchamber 92 is defined by horizontal foraminous members 96 and 97 whichextend, respectively, from wall 93 to the top of each of half cathodes79 and of vertical side walls 82. The lower enclosure of inner chamber92 is substantially the same as the top enclosure and is defined byhorizontal foraminous members 98 and 99 which extend, respectively, fromwall 93 to the bottom of each of half cathodes 79 and of side walls 82.

The various walls of the unit 10 including casing 83, wall 93 andforaminous tubular cathodes 80, foraminous half cathodes 79 and top andbottom foraminous horizontal enclosing members 96, 97, 98 and 99, aresecured within this unit and are formed of an electrical conductor suchas a metal, usually steel, nickel or stainless steel. Direct current issupplied to current distributing means 34 via a cathode bus. Theindicated forarninous surfaces are conveniently in the form of a screen(as shown) although it is to be understood that the term foraminous isalso intended to include expanded metal sheet, perforated metal sheet aswell as porous metal formed from sintered powder. The various formanioussurfaces of the cathodic section are in association with diaphragm 103formed of any suitable liquid permeable or porous material which ischemically inert to the aqueous electrolyte medium which is circulatedbetween the opposing anodic and cathodic surfaces. Typical examples ofsuitable materials of which the diaphragm may be formed are asbestos,polyethylene, polypropylene, polytetrafluoroethylene,phenol-formaldehyde polymers and other such materials. These diaphragmmaterials may be used in Woven form and in the form of mats, felts,paper, yarn and bonded fibers. The diaphragm may also be a compositeprepared from either a natural or synthetic fiber in any one of theaforesaid forms onto which fiber there is first polymerized a differentpolymer followed by removal of the original 8 fiber to createcapillaries in the original form, the resulting capillariessubstantially increasing the permeability and surface area of the finalcomposite.

Top section 15 of the cell of FIGURE 5 comprises dome 109 having inlets112 therethrough and outlet 114. As shown, the dome is made of cement orconcrete and is lined with protective layer 116 to avoid erosion of thelower surface. Protective layer 116 may be composed ofpolytetrafiuoroethylene plastic which is laminated or impregnated withglass or asbestos cloth and is bonded to the cement surface of the domeby an epoxy resin. The liner may also be composed of moldedpolyethylene, polypropylene, etc., of the same contour as the innersurface of the dome, or the dome itself may be of a single mold ofpolymeric material such as polyethylene, polypropylene,poly-methacrylates, etc.

The three units 5, 1i) and 15 are mounted one above the other and areheld tightly together by their weight. When the unit cell is designedfor smaller product capacity, the sections are held in place by bolts. Aliquid and gas tight seal is provided between the units by gasket 106comprising an inner core 108 formed of asbestos, rubber or otherresilient material and an outer layer 1437 formed of a synthetic polymersuch as polyethylene, polypropylene, polyacrylonitrile,polytetralluoroethylene and other such materials which are electricalinsulators and essentially non-corrosive. When the cell is designed fora relatively large product capacity and is operated at substantiallyatmospheric pressure usually no further securing means other than theweight of the middle and top units is required. When the cell isoperated under a substantial pressure, however, it may be necessary tosecure the three units by bolts, clamps or other such pressure securingmeans. The cell is elevated above floor level and is supported bysupport legs 90 which are fastened to lower section 5. Support legs 90are composed of an electrically insulating and non-conductive materialsuch as a ceramic, cement, bricks, etc., or are formed of anelectrically conductive material such as steel having an insulatorthereon.

In operating cells provided with the platinized metallic electrodes ofthis invention such as the cell illustrated by FIGURE 5, a fluidreactant such as ethylene or propylene is fed to inlet 31 such that thereactant is distributed through chamber 32 within base unit 5. Thereactant is confined within base unit 5 such that it flows freelythrough openings 44 in reinforcement brackets 43 upwardly into innerchamber 11 of each of platinized anodes 2. Aqueous medium containing adissolved metal halide electrolyte such as any of the alkali metalchlorides for example, is fed to the inner cell chamber by means ofinlet 112 within dome 109 such that it flows downwardly between theouter surfaces of the anodes and diaphragm 103 on the foraminouscathodic surfaces which include half cathodes 79, tubular cathodes andside Walls 82. A cathode bus connector (not shown) fitted to currentdistributing means 84 of cathodic unit 10, is connected to the negativepole of a direct current rectifier such that the current flows throughcurrent distributing means 84, casing 83, wall 93 and the foraminoussurfaces of unit 10. Anode bus connector 46 is tied to the positive poleof a direct current rectifier and the current flows through currentdistributing plate 35, anodizable metal layer 36 and anodes 2, the baseof the anodes being in contact with these two metal layers. Theanodizable metal layer 36 composed of at least one of titanium,tantalum, zirconium or niobium constitutes the bottom or floor of theinner cell chamber, and the top surface of the metal is thus in contactwith aqueous medium which is fed to the inner cell chamber. As theelectrical current flows through anodic current distributing plate 35during operation of the cell, the surface of the titanium, tantalum,zirconium or niobium of layer 36 which is in direct contact with theaqueous electrolyte medium, is converted in the presence of the aqueousmedium to the corresponding metal oxide which is not corroded or erodedby the aqueous medium. In this manner, an adherent, continuous,protective film of metal oxide is formed on the top surface of metallayer 36 thereby avoiding the necessity of coating the floor of theinner cell chamber with a protective layer of an extraneous nature suchas epoxy resin as is necessary when the exposed surface of the base isformed of concrete, cement or a ferrous metal. Similarly anyunplatinized surface of the substrate metal of base 14 and top member 13of anodes 2 which may be in direct contact with aqueous medium is alsoconverted to the corresponding metal oxide. The anodization of theunplatinized titanium, tantalum, zirconium or niobium surfaces of thebase unit which are in contact with aqueous medium occurs spontaneouslywhen the direct current is applied during operation of the cell asdescribed herein. Alternatively, the conversion of such anodizable metalsurfaces to the corresponding oxide may be effected prior to actualoperation of the cell by applying a high voltage to the unit until thecurrent ceases to flow. It is to be understood that although thoseportions of the unplatinized substrate metal surfaces of the anodeassemblies described herein which are in direct contact with aqueousmedium, are converted to a protective film of metal oxide such astitanium dioxide, the unexposed surfaces remain in the conductiveelemental form.

In operating the cell with a metal halide as the dissolved electrolytewhile feeding olefin to the anolyte, the direct current is supplied tothe cell at a current density of between about 50 and about 500 amperesper square foot of apparent electrode surface. Under these condi tionsthe potential drop across the anode bus and cathode bus is between about2.8 and about 5.5 volts which under any given set of conditions, issubstantially less than the potential drop across the cell provided withanodes formed of carbon.

As the olefinic reactant passes upwardly into the inner anode chambers,it diffuses through the platinized-metal substrate side walls 12 ofanodes 2 and reacts at the metal anode-anolyte interface to form thecorresponding halohydrin derivative of the olefin in the anolyte. Theaqueous medium containing the halohydrin derivative passes throughdiaphragm 103 on the foraminous cathodic surfaces of tubular cathodes 80into cathode compartments 85 and also passes through the diaphragm onthe peripheral foraminous walls of the inner cell chamber, i.e., endwalls 101 of half cathodes 79 and side walls 82, into inner peripheralchamber 92 which, as described above, is enclosed by top foraminoushorizontal walls 96 and 97 and lower foraminous horizontal walls 98 and99. The halohydrin reacts with the alkaline catholyte contained incompartments 85 and 92 to form olefin oxide product. Hydrogen whichforms on the cathodic surfaces is confined within cathode compartments85 and 92 by diaphragm 103 such that it is substantially prevented frompassing into the vapor space above the level of the aqueous medium. Thecatholyte which contains olefin oxide product and cathode gasescomprising hydrogen and vapors of olefin oxide product, whensufficiently volatile, pass through openings 94 in wall 93 into outerperipheral chamber 91. The cathode gases exit from chamber 91 by meansof upper outlet 117 and the catholyte is withdrawn from the cell bymeans of outlet 118. Anode gases containing any unreacted olefin,halogenated olefin, water vapor, etc., rise through the anolyte and intothe vapor space above the level of the aqueous medium and exit from thecell by means of outlet 114 within the dome.

As stated above, lower section 5 of the cell of FIG- URE 5 is a separatecomplete unit into which the metallic electrodes of this invention arefitted and, although lower section 5 is shown provided with particularelectrodes 2 of FIGURE 1, it is to be understood that lower section 5may also be provided with electrodes 4, 6 and 8 of FIGURES 2, 3 and 4,respectively, in place of electrode 2. For example, in fitting electrode4 of FIGURE 2 in lower section 5 of FIGURE 5, L-shaped base 16 ofelectrode 4 is also fitted within the slotted double metallic layer 34such that the horizontal portion of base 16 is secured to the lowersurface of current distributing plate 35. This latter arrangementprovides additional support for the electrode and is especially usefulwhen the porous side walls are of relatively thin dimension. Similarlybase 19 and base 28 of electrodes 6 and 8 of FIGURES 3 and 4,respectively, may he slipped into slots 37 in double metallic layer 34and fixed in place by welding. Although side walls 12 of electrodes 2, 4and 6 and side walls 26 of electrode 8 are porous above the baseportion, it is to be understood that only a portion of the side walls ofthe hollow blade type of anode need be porous as illustrated byelectrode 54 of FIGURE 6 to which reference is now had.

Electrode 54 of FIGURE 6 is in the form of a hollow blade comprisinginner support means 62 and inner chamber 61 which is enclosed by topenclosure 59 and vertical side walls 55. The latter are sectioned into anon-porous base 58 and non-porous upper section 56 with porous section57 therebetween. Side walls 55 and top enclosure 59 are formed of one ofthe substrate metals, e.g., titanium, and although the entire hollowblade may be platinized, it is only necessary to platinize the surfaceof the substrate metal which is exposed to the aqueous medium andopposed by a cathodic surface during operation in an assembled cell suchas section 55, as well as any portion of porous section 57 which mayoppose a cathodic surface in order to maximize the reactive anodicsurface area. Top enclosure 59 is as described above with reference totop enclosure 13 of electrode 2 of FIGURES 1 and 5. Electrode 54 ofFIGURE 6 is shown fitted within a base which is the same as section 5 ofFIGURE 5 except that it is provided with an insulating layer 47 aboveand about the periphery of anodizable metal layer 36. Layer 47 iscomposed of an electrically insulating and non-conductive material whichis suitably cement, plastic, glass, etc., and is held between verticalmembers 48 and 49 which together with the upper surface of the endportion of anodizable metal layer 36 form a pan-shaped container. Outervertical member 48 may be formed of any rigid solid such as steel andmay be an integral part of connecting plate 41 to form an L-shapedmember which is provided on one side with an opening through whichcurrent distributing plate 35 may extend, an anode bus being connectedto the extended portion such as illustrated by FIGURE 5. Inner sidemember 49 is formed of at least one of titanium, tantalum, zirconium orniobium and is also anodized either prior to or during operation of thecell, such that a non-corrosive film of the corresponding oxide formsthereon to provide a protective surface continuous with the metal oxidewhich also forms on metal layer 36. The top surface of insulating layer47 is provided with gasket 51 having inner core 53 surrounded by layer52 as described above in connection with gasket 106 of FIGURE 5, uponwhich any suitable cathodic unit may be mounted such as unit 10 of FIG-URE 5. In such a cell, the olefin reactant is fed to inlet 31 of thebase of the cell such that the olefin flows freely through chamber 32and upwardly into the inner chamber 61 of electrodes 54 which functionas the anodic electrode. In view of the fact that only a portion of sidewalls 55 is porous, the olefin passes through only porous section 5-7and passes upwardly through the anolyte wherein it is converted tohalohydrin. The operation of a cell provided with the anode assembly ofFIGURE 6 is otherwise the same as described above with respect to FIG-URE 5.

Although the anodic electrodes of FIGURES 16 are in the form of hollowblades such that the olefin reactant is fed to the inner chambersthereof, it is to be understood that the particular electrodes used incarrying out my process may comprise a solid, non-porous blade asillustrated by FIGURES 7, 8 and 9. Each of electrodes 63, 68 and 74 ofthese figures comprises blades 64, 69 and 78, respectively, formed of acore of the substrate metal such as titanium, having at least one of theaforesaid platium group metals as a continuous coating on the surfacethereof. In each instance, the platinized-titanium blade isperpendicular to and extends upwardly from a base or supporting meanswhich is preferably formed of one of the substrate metals. Usually atleast a portion of the support for the solid, non-porous blade is poroussuch that it may also function as the means by which the olefinicreactant is fed into the anolyte. For example, the base of electrode 63of FIGURE 7 is horizontal plate 66 which is fitted directly to the topsurface of anodizable metal layer 36 and over slots 37 in layers 36 and35 which are as above described. In this manner, olefin reactant passesfrom chamber 32 through porous surface 66 and upwardly along the outersurface of blade 64. The other members of FIGURE 7 are as describedabove in connection with FIGURE 5 except that the base is provided witha peripheral insulating layer 47 as described above in connection withFIGURE 6 with the further modification that insulating layer 47 isprovided with O-ring seals 67 formed of a fluid impervious material tofurnish a fluid tight seal between the base and cathodic unit mountedthereon. For example, seals 67 may be formed of asbestos or glass fiber(in the form of rope, cloth or sheet) impregnated or laminated withpolytetraiiuoroethylene plastic, phenolformaldehyde resins, etc., or theseals may be formed of a resilient center of asbestos, rubber or resins,covered with a continuous thin sleeve of material which is not attackedby the aqueous medium of the cell such as polyethylene, polypropylene,polyacrylonitrile and the like.

The base of electrode 68 of FIGURE 8 is different from that of FIGURE 7in that horizontal plate 70 to which blade 69 is secured is elevatedabove double met'ah lic layer 34 by vertical members 71 which are inelectrical association with current distributing plate 35 and substratemetal layer 36 by means of members 72. Since blade 69 is the reactiveanodic surface only it need be platinized and the support meansincluding 70, 71 and 72 which are formed of one of the substrate metalssuch as titanium need not be platinized. One or both of 70 and 71 whichenclose chamber 73 may be porous and, as shown, only vertical members 71are porous. The support means of electrode 74 of FIGURE 9 is the same asthat shown by FIGURE 8 except that horizontal plate 75 is porous whereasvertical members 76 are non porous. The remainder of the anodic unit ofFIGURES 8 and 9 may be as shown by FIGURE 5, 6 or 7 and, in each case,the olefinic reactant which is fed to chamber 32 from an external sourcepasses therefrom into smaller chambers 73 and 77, respectively, ofFIGURES 8 and 9, through respective porous metallic members 71 and 75,directly into the anolyte wherein the olefin reacts along the platinizedtitanium surface of anodic blades 69 and 78.

It is to be understood with reference to electrodes 63, 6S and 74 ofFIGURES 7, 8 and 9 respectively, that although the respective supportingmeans of the solid anodic blades need not be platinized, any portionthereof may be coated with the platinum group metals without departingfrom the scope of this invention. When not platinized, the outersurfaces of the supporting means which are in direct contact with theaqueous electrolyte medium are readily converted to a coating of theoxide of the substrate metal of which they are formed such as titaniumoxide, either prior to or during operation of the cell.

It is to be understood that various other modifications of the anodicsections illustrated by FIGURES 5-9 may be made Without departing fromthe scope of this invention. For example, although FIGURE 5 showsintroduction of the aqueous medium to the cell by means of inlets 112positioned within the dome the aqueous medium may be fed to the cell bymeans of inlets positioned within the base of the cell, This latterembodiment is illustrated by accompanying FIGURE 10.

The anode assembly of FIGURE 10 comprises electrode 6 described abovewith reference to FIGURE 3, current distributing plate 122 havingsubstrate metal layer 121 thereon, each of the latter having alignedslots 134 therethrough, inlets 123 which extend upwardly through the twolayers of metal, and chamber 124 enclosed by base plate 126 and sidewalls 127. As shown, base plate 126 is provided with at least one inlet128 by means of which the olefinic reactant which is to be contactedwith electrode 6 is fed to chamber 124, although it is to be understoodthat such inlet may also be positioned within side walls 127. Inlets 123are also formed of one of the substrate metals such as titanium, suchthat a continuous surface of such metal exists between these inlets andmetal layer 121 and are the means by which the aqueous electrolytemedium is fed to the cell. Inasmuch as inlets 123 are also in contactwith current distributing means 122 they are anodic and, since they areexposed to aqueous medium during operation of the cell, the exposedsurface of the substrate metal, i.e., titanium, tantalum, zirconium orniobium, is converted to corresponding metal oxide as is the exposedsurface of layer 121 such that a continuous surface of the non-corrosivemetal oxide such as titanium oxide, is provided. This anode assembly isalso provided with a peripheral insulating layer 132 contained Withinpan-shaped member 1.33 which is usually formed of steel. As shown,current distributing plate 122 extends downwardly at one side andextension 129 thereof serves as the anode terminal. Extension 129 isconnected to anode bus connector 131 which in turn is connected to thepositive pole of a direct current rectifier.

As illustrated by the electrode structures of the above discussedFIGURES l-9, the anodic electrodes of this invention may be in the formof a solid blade, i.e., a nonporous blade, such as those designated bynumerals 64, 69 and 78 of FIGURES 7, 8 and 9, respectively, or at leasta portion of the electrode may be porous as in the case of the hollowblades illustrated by FIGURES 1-6. In either case, the reactive surfaceof the electrode is for-med of one of the substrate metals such astitanium having a continuous layer of platinum group metal on theexternal, visible surface as well as on the internal surface contributedby any porous area. It is to be understood that the term reactivesurface as used herein in describing the anodic electrodes of thisinvention refers to that portion of the electrode which opposes acathodic surface during its use as described herein.

The platinum group metal may be applied to the substrate metal by avariety of techniques such as coating the surface of the substrate metalwith a salt of the platinum group metal followed by firing to decomposethe salt to elemental metal; chemical and electroless plating;electrodeposition including electroplating and brush or pad-wheelelectroplating; vacuum deposition; as well as mechanical bonding methodssuch as cladding or lamination techniques. The particular methodemployed depends on the physical state of the substrate initially aswell as on the desired physical state of the final reactive surface ofthe electrode, that is, porous, non-porous or various degrees of poroussurface areas on a solid metal core.

When used in porous form, the substrate metal may be prepared bysintering of the metal in powder form in an inert atmosphere or undervacuum at an elevated temperature such as about 8-00-1500" C. Thesubstrate may also be prepared in porous form. from a knitted mesh (asopposed to woven screen) formed of about l-3 mils diameter Wire of thesubstrate metal which mesh is compressed in a mold into a matrix ofcontrolled porosity, followed by sintering at an elevated temperature;the sintered matrix of wire is then preconditioned and coated with theplatinum group metal as described herein. Another similar matrix of thesubstrate may be formed by compressing in a mold several layers of finescreens for-med of the substrate metal such as titanium and the compactor compressed composite is then sintered at an elevated temperature andsubsequently coated with the platinum group metal. Suitable propertiesof porous titanium, for

example, for use in the manufacture of the porous elec trodes describedherein are given in the following Table I:

TABLE I.PROPERT'IES OF POROUS TITANIUM MATRIX Porosity percent -70 Porepeak microns 0.1-50 Bubble pressure in water p.s.i 2-16 Permeabilitymil-lidarcies -500 Resistivity micro-ohm-cm 4-2-80 A particularlypreferred form of porous titanium is that having the followingcombination of the above properties: a porosity of 40 percent; a bubblepressure in water of from 1.8 to 5.4 p.s.i.; a permeability of from 100to 150 millidarcies and a resistivity of from 200 to 280 microohm-cm.

In combining the platinum group metal with the substrate in eitherporous or non-porous form, the surface of the substrate is subjected topreliminary conditioning to free it of grease, and otherwise wash itsuch as by degreasing with an organic solvent such as carbontetrachloride and trichloroethylene. The degreasing of fine porositytitanium frequently requires further treatment such as continuous vapordegreasing with trichloroethylene, for example, by which the poroussubstrate is exposed to vapors above 'a refluxing bath of degreasingagent. The surface of the substrate onto which the precious group metalis to be deposited is further treated to ensure re moval of any highlyresistive metal oxide or carbonate which may be present on the surface,by electrical or chemical etching. Chemical etching is accomplished bytreating the substrate in an acid bath such as hydrofluoric acid, nitricacid or hydrochloric acid or mixtures thereof. Electroetching is usuallycarried out in media such as hydrochloric acid, oxalic acid, citricacid, hydrofluoric acid alone or in combination with ammonium fluoride,sulfur-containing acids such as sulfuric, sulfonic, and sulfamic acids,or in molten media of alkali metal compounds such as sodium hydroxide,sodium chloride, sodium fluoride, etc. It is preferred to etch thesubstrate in a solution which will require minimum subsequent washingwith Water prior to platinum coating in order to avoid partiallyoxidizing the substrate surface with oxygen contained in the water. Thetreating solutions are circulated through any portion of the substratewhich is porous and which will constitute a reactive surface in thefinished electrode so as to provide a freshly exposed surface throughoutthe area on which the platinum group metal is to be deposited includingthe surface of any internal pores. The cleaned and etched surface of thesubstrate is subsequently subjected 0t any one of a number of methods todeposit the platinum group metal.

It is noted, however, that platinumcoating methods produce a poroussurface which is dependent on the degree of etching to which the metalsubstrate is subjected and, since platinum plating baths in general havea fair throwing power, the platinum group metal coating may be of arelatively high degree of porosity especially in the recessed areas ofthe etched surface. As already disclosed hereinabove, the metallicelectrodes described herein may also comprise a third metallic componentreferred to herein as the undercoat which may be applied to the etchedsurface of the substrate prior to deposition of the platinum groupmetal. Thus a uniform layer of the metallic undercoat may be appliedeither by electrodeposition or by spraying or brushing a metal salt or amixture of metal salts onto the substrate followed by decomposition ofthe salt at an elevated temperature to convert the salt to elementalmetal .The composite may then be further treated, particularly after theplatinum group metal is deposited, at a high temperature to bind theundercoat to both the substrate and platinum group metals by forming analloy of the undercoat with each metal by diffusion.

A particularly preferred method for depositing the platinum group metalonto the surface of the substrate is electroplating which isaccomplished by placing the preconditioned substrate metal as thecathode in a standard electroplating bath containing a salt of theplatinum group metal, opposed to an anode formed of platinum, platinizedtitanium or steel and passing an electric current therethrough. Forexample, in depositing platinum, suitable electroplating baths aresolutions based on platinic chloride, platinum-diammino-dinitrite (knowncommercially as platinum P salt), alkali hydroxy-platinates,nitrito-platinites and platinurn-diammino-nitrate. Typical examples ofsuch platinum electroplating solutions are: (l) a solution of platinicchloride in hydrochloric acid; (2) solutions prepared by reactingplatinic chloride (e.g., 5 grams per liter) with an excess of a mixtureof ammonium and sodium monohydrogen phosphates; (3) solutions obtainedby dissolving platinum-diarnmino-dinitrite in aqueous solutions ofconcentrated sulfuric, phosphoric or sulfamic acids such as a sulfamicacid solution containing from 8 to 15 grams of platinum metal contentderived from the dinitrite salt; (4) solutions ofplatinum-diamrnino-dinitrite containing a combination of sodium nitriteand ammonium nitrate or sodium acetate and sodium carbonate; (5)alkaline solutions of hexahydroxy-platinic acid such as those containingsodium and potassium hy droxides or potassium sulfate, the platinic acidin these alkaline solutions being in the form of the correspondingalkali metal hexahydroxy-platinate salt; and (6) a di ammino-nitratebath containing 4 to 9 grams of platinum maintained slightly ammoniacalby the addition of ammonium hydroxide. In using these solutions, theplating is effected at a current density between about 10 and aboutamperes per square foot of electrode surface and the bath is usuallymaintained at a temperature between about 50 and about 100 C. The metalis usually electroplated at a plating rate of 10-30 milligrams perampere-minute. For example, the thickness of the metal coating plated ata rate of 1 milligram per square inch is about 3 micro-inches.

Another suitable electrical plating technique is brush plating wherebythe substrate metal is made cathodic and a solution of a compound of theplatinum group metal is applied thereto by means of a brush or pad. Forexample, in applying platinum to titanium by this technique, thetitanium is made cathodic, the handle of the plating pad is madeanodi-c, and the pad is dipped into the platinum plating solution andapplied to the titanium surface with a rubbing action. One advantage ofbrush plating is that it involves simple equipment and, because of theproximity of the anode to the titanium surface, a more adherent anduniform coating of the platinum is obtained which is especiallyadvantageous when the substrate is of irregular shape. Brush plating isused satisfactorily to coat a solid or nonporous surface of thesubstrate metal and may be used to coat the internal surface of a porousmatrix provided the plating is carried out with circulation of theplating solution through the pores.

Another suitable method which may be used in the manufacture of theelectrodes of this invention is chemical or electroless plating. Thismethod is satisfactorily employed for the coating of the substrate metalin non porous or porous form. A suitable electroless platinum platingbath is an ammoniacal solution of platinum-diammino-dinitrite containingethylene-dinitrito-tetraacetic acid as a chelating agent.

The surface of the substrate may also be coated with the platinum groupmetal by vacuum deposition. For example, in depositing platinum by thistechnique, the substrate metal such as titanium as either a solid plateor porous matrix is immersed in and impregnated with a platinum chloridesolution or chloroplatinic acid under a sub-atmospheric pressure and thesubstrate so treated is subjected to an elevated temperature such asbetween about 500 and about 1000 C. such that the platinum is depositedin finely divided form and dispersed throughout the pores of a porousmatrix.

In the case of preparing the reactive anodic surface in 15 porous form,however, it is usually preferred to deposit the platinum group metal byelectroplating, brush plating with fiow through of solution, orelectroless plating as described above. A porous matrix is usuallycoated by these techniques because they more readily provide asubstantially even distribution of the platinum group metal through thepores of the matrix at an amount of platinum just sufficient tocompletely coat the surface of the matrix, without plugging the pores,and thus allow for the diffusion of the olefinic reactant which is to bebrought into contact with the anode during use in the operating cell.

When the surface to be coated is nonporous, in addition to the abovetechniques, other methods which are suitably employed are immersioncoating and brush firing. For example, in accordance with immersioncoating and brush firing, the preconditioned surface of titanium isdipped in or brushed with, respectively, a saturated solution ofchloroplatinic acid with or without the presence of a reducing agentsuch as hydrazine, followed by drying to remove the solvent, and firingto decompose the platinum compound to metallic platinum. The procedureof immersing or brushing, drying and firing is repeated until thedesired thickness of the platinum coating is obtained. The firing stepis carried out above the decomposition temperature of the precursor ofthe platinum group metal which in the case of chloroplatinic acid isabout 500 C.

It is to be understood that in the above described deposition techniquesfor preparing the reactive surfaces of the anodic electrodes describedherein, in place of the indicated platinum precursor compounds,corresponding compounds of the other platinum group metals may beemployed such as palladium-diammino-dinitrite; palladous chloride;sodium chloropalladite; tetra-ammino palladous chloride; rutheniumnitrosyl-chloride; ruthenium sulfamate; ammonium chloro-iridate; rhodiumsulfarnate; and rhodium sulfate.

Another method by which the nonporous electrodes of this invention maybe formed is mechanical bonding which comprises cladding thin foils ofthe platinum group metal or alloys thereof on the substrate metal.

It is to be understood that although the reactive surface of the anodicelectrodes are composed of the substrate metal having a continuous layerof platinum thereon, other portions of the complete electrode asassembled in an operating cell need be composed of the substrate metalonly. As described above, the complete hollow blade type electrodesillustrated by FIGURES 1-4, include a top enclosure and a base portionwhich is secured to the anodic base assembly. In the manufacture of suchelectrodes, the hollow blade of desired shape is usually first formed ofthe substrate metal only and those portions such as the top enclosureand base portion which need not be platinized may be masked during theabove described techniques for depositing the platinum group metal, sothat the latter metal is deposited only on that portion of the substratewhich becomes the basis of the reactive anodic surface.

The amount of platinum group metal deposited on the substrate metal isrelatively small and is usually just sufiicient to be a continuous filmon the reactive surface. Generally, the platinum group metal constitutesbetween about 0.5 and about 5, more usually between about 0.7 and about1.0, weight percent of the total weigth of the reactive surface of theelectrode. The thickness of the platinum group metal layer on thesurface of a nonporous substrate is usually between about and about 400micro-inches. The thickness of the layer of platinum group metal on thesurface of a porous matrix including the surface of the internal pores,varies depending upon the porosity of the substrate and is limited tothe extent that the pores are not plugged 'by metal. The pores of aporous matrix usually have a diameter of between about 0.3 and aboutmicrons and a mean pore size of between about 3 and about 4 microns. Thethickness of the platinum group metal coating on the porous surface isbetween about 10 and about 200 micro-inches although a thicker coatingmay be applied without departing from the scope of this invention. Otherproperties of the porous electrodes prepared as typically describedherein are a porosity of between about 15 and about 40 percent, a bubblepressure of between about 2 and about 10 inches of mercury, and aresistivity of between about 200 and about 280 micro-ohmcm. Theseproperties of the platinized porous substrate are obtained by properselection of the matrix which is to be platinized except that thepermeability of the structure usually increases by about 20 to 40percent during preconditioning treatment prior to applying the platinumgroup metal by the above-described deposition techniques such aselectroplating. On the other hand, the resistivity and other propertiesof the platinized surface are substantially the same as that of theporous substrate metal.

The following examples are offered as a better and further understandingof the teachings of this invention and, since they are intended astypical and illustrative they are not to be construed as unnecessarilylimiting thereto. Except as otherwise indicated, the cells in whichthese specific examples are carried out are of the type illustrated byFIGURES 11 and 12 or modified forms thereof.

The cell of FIGURE 11 comprises outer vertical wall 146 provided withanode terminus 142 and outer wall 141 provided with cathode terminus143. These outer walls are separated by sections 147 to which anode 152is connected, spacers 144, and sections 146 to which the cathodic screen149 is connected, the various sections 141, 146, 144 and 147 havingfluid tight gaskets therebetween. Anode 152 is in association with afine knitted nickel screen 153 which is crimped to provide a large areaof contact and is in contact with a coarse screen 154 of stainless steelwhich provides pressure against crimped screen 153 to obtain goodelectrical contact. As illustrated, screen 149 is in association with afluid permeable diaphragm 151 such as asbestos, polyethylene orpolypropylene. The cell is further provided with various inlets andoutlets by means of which the olefin and brine feeds are fed to the celland 'by means of which anodic and cathodic gases and aqueous medium arewithdrawn from the cell. For example, aqueous medium such as an aqueoussolution of sodium chloride is fed to the cell from an external sourceby means of inlet 158, passes through inlet 159 such that it isdischarged into anode compartment 163 flowing upwardly between theopposing surfaces of anode 152 and diaphragm 151. Olefinic feed such asethylene or propylene is fed to the cell by means of inlet 157, passesthrough foraminous sparge 156 which may be formed of porouspolyethylene, porous glass or porous anodized titanium, and flowsupwardly into the anolyte contained in anode compartment 163. When thechlorohydrin derivative of the olefin is dehydrochlorinated within thecell, it is necessary to provide for the fiow of anolyte throughdiaphragm 151 into cathode compartment 164 wherein the chlorohydrin isdehydrochlorinated in the alkaline catholyte. This necessary flow isachieved by feeding the aqueous solution to the anode compartment 163and by withdrawing the catholyte from the cell from cathode compartment164 by means of outlet 161. When sufficiently volatile under theconditions at which the cell is operated, the oxide such as ethyleneoxide or propylene oxide, passes from the cell as cathodic overhead bymeans of outlet 148, the remainder of the oxide dissolved in thecatholyte being withdrawn from the cell by means of outlet 161. Volatileproducts formed in the anolyte such as dichlorinated derivatives of theolefin, pass from the cell by means of outlet 162, and other cathodicgases such as hydro-gen exit from the cell by means of outlet 148.

The cell of FIGURE 12 is similar to that of FIGURE 11 except thatinstead of being provided with means by which the olefin is fed througha sparge directly into the anolyte, the cell is provided with olefininlet 176 by means of which the olefin is fed to chamber 182 enclosedbetween outer wall 166 and porous anode 172, the latter having anodeterminus 173 connected thereto. In this manner, the olefin reacts at theinterface of porous anode 172 and the anolyte contained in anodecompartment 183, aqueous medium being fed to the anode compartment bymeans of inlet 177. The anolyte flows through fluid permeable diaphragm171 in association with cathodic screen 169 having cathode terminus 174,into the cathode chamher 184 between cathodic screen 169 and outer wall167. Catholyte is withdrawn from the cell by means of outlet 178 andcathodic and anodic gases exit from the cell by means of outlets 179 and181, respectively. The cathodic and anodic sections of the cell areseparated from one another by means of spacers 168 which are formed ofany suitable electrically insulating material such as glass,polyethylene and the like. Fluid tight seals are provided between thesections of the walls of the cell by suitable gaskets, and the endportions of cathodic screen 169 are imbedded in an epoxy resin.

When it is desired to recover the halohydrin as such the cells ofFIGURES 11 and 12 are modified by positioning between the opposinganodic and cathodic surfaces a substantially fi-uid impervious barriersuch :as porous sintered glass or asbestos paper or mats of sufi'icientthickness to prevent the flow of aqueous medium between the anode andcathode compartments, in place of fluid permeable diaphragms 151 and171, respectively. Additionally, the cells are further modified toprovide an outlet in the anode compartment by means of which anolyte iswithdrawn from the respective anode compartments, and the cathodecompartments are provided with an inlet by means of which aqueous brinesolution may be fed thereto directly from an external source. By thesemodifications, the halohydrin may be recovered as such from the celland, in view of the fact that the reaction which occurs in the anolyteis improved by the use of the electrodes described herein as the anodicsurface, the method also constitutes an improved method for themanufacture of halohydrins.

EXAMPLE I Platinization of porous titanium was conducted in anelectroplating cell comprising a plastic housing and fitted withvertically mounted electrodes. The anode consisted of platinum in theform of a screen and extended the full height of the interior of thecell. The cathode also extended the height of the cell interior and wasformed of a plaque of porous titanium having 20 percent porosity, apermeability of 103 millidarcies and a resistivity of 269 micro-ohm-cm.Prior to mounting in the cell, the porous titanium plaque was degreasedin trichloroethylene, pickled in concentrated hydrochloric acid at 50-55C. for five minutes and then rinsed thoroughly in distilled water. Theplatinum electroplating solution was a standard commercially availablesolution containing approximately eight grams of platinum per liter ofsolution and called Platanex III-LS available from Sel-Rex Corporation.This solution was flowed through the cell such that it first passedthrough the anodic platinum screen into the area between the opposinganodic and cathodic surfaces, through the porous titanium cathode andthen out of the cell. Using this apparatus, the electroplating bath, ata temperature of 82 C., was continuously circulated through theelectrodes at a solution flow rate of 265-300 cc. per minute for onehour during which time a 2 inch by 5 inch area of the cathode was platedwith platinum at a current density of approximately amperes per squarefoot of apparent cathode area. At the end of this run about 0.476 gramof platinum was distributed on the porous titanium surface. Theplatinized titanium was then degreased, pickled and rinsed under theaforesaid conditions and additional platinum was deposited bycirculating the electroplating solution at a temperature of 65-78 C.through the electrodes at a solution flow rate of 50 cc. per minute anda current density of approximately 10 amperes per square foot ofapparent cathode area. The total amount of platinum deposited during.these two consecutive runs was 1.489 grams, the finished electrodehaving a permeability of millidarcies and a resistivity of 271micro-Ohm-cm. This electrode is designated herein as Anode A.

EXAMPLE II In carrying out the procedure of this example, a substrate ofporous titanium was employed having a mean pore size of about 2.8microns with a pore size range of 1.5-4 microns and a porous metalporosity of 19.5 percent. The substrate was electrocleaned using astandard cleaning solution, rinsed in distilled water and then assembledas the cathode in a fiow through electroplating cell of the typedescribed in Example I above. A 6 normal solution of hydrochloric acidwas flowed through the cell as described in Example I, at roomtemperature followed by continuous washingwith a 12 normal hydrochloricacid solution until the evolution of gas was first observed at whichtime the cell was drained of liquid. Three liters of boiling distilledwater were then passed through the cell, the cell drained, and a strikeof platinumfrom a standard electroplating solution containingapproximately 12 grams of platinum per liter of solution was appliedover a period of 5 minutes at 3 amperes at a flow rate through the cellof electroplating solution of approximately cc. per minute, the currentdensity being 21 amperes per square foot. The titanium substrate wasthen electroplated for another period of approximately 35 minutes at 1.7amperes, 1.9 volts, a flow through rate of the electroplating solutionof 50-80 cc. per minute and a current density of 12 amperes per squarefoot. The current was then cut off, the cell drained immediately and thesample rinsed and boiled in distilled water. This electrode isdesignated herein as Anode B.

EXAMPLE III The substrate employed was porous titanium having a metalporosity of 26.7 percent and a bubble pressure of 9.5 inches of mercuryin the form of a hollow cylinder (3 inches in length and having a /2inch diameter). The porous titanium cylinder was treated by immersion invarious solutions, drawing the solutions through the porous surface bysuction. Thus the cylindrical porous titanium substrate was immersed forelectro-cleaning in a standard cleaning solution followed by immersionin distilled water. The cylinder was then immersed in a 6 normalhydrochloric acid solution at room temperature followed by immersion ina 12 normal hydrochloric acid solution until the evolution of gas wasfirst observed and was then rinsed in boiling, distilled water. Thecleaned substrate was next immersed in a warm (about 60-80 C.) platinumelectroplating solution containing approximately 15 grams of platinumper liter of solution and was opposed by a platinum anode.Electroplating was carried out for one minute at 30 amperes per squarefoot and for 1 9 minutes at 20 amperes per square foot, followed byrinsing of the electroplated surface with distilled water. Thiselectrode is designated herein as Anode C.

Example IV Anode A was mounted as anode 172 in an electrochemical cellof the type illustrated by FIGURE 12, the diaphragm 171 separating theanode and cathode compartments being formed of white asbestos. Anode Awas connected to the positive pole of a direct current rectifier bymeans of anode terminus 173 and was opposed by a stainless steel screen169 connected to the negative pole of the rectifier by means of cathodeterminus 174. Aqueous solution containing 90 grams per liter ofdissolved sodium chloride was fed to anode compartment 183 at a flowrate of 11 cc. per minute. Propylene was fed to the back of porousplatinized titanium Anode A (chamber 182) at a rate of 340 cc. perminute. The cell was ope-r- 19 a'ted at a temperature of 110 F., acurrent density of 140 amperes per square foot for a period of 4 hours.The voltage drop across the cell remained constant during operation andwas 4.1 volts. Propylene chlorohydrin forms 20 results of a series ofruns are given in which propylene was reacted in a cell of the typeillustrated by FIGURE 12 except that a fluid impermeable barrier (glass)was positioned between the anode and cathode in place of fluid in theanolyte and passes through the diaphragm 171 into permeable diaphragm171 such that anolyte was subthe cathode compartment wherein it isdehydrochlorinatstantially prevented from reacting in the alkalinecathoed in the alkaline catholyte forming propylene oxide. lyte. 'Ilhecell is further modified to allow for withdrawal Efiluent gasescomprising propylene oxide and cathodic of anolyte from the anodecompartment and feeding of hydrogen exiting from the catholyte by meansof outlet aqu ous Solution to th Cath Compartment from an 179, werecollected and analyzed. Catholyte which also external source. In thismanner, a separate flow of aqueous contains dissolved propylene oxideproduct was with medium is maintained in and out of the anode chamberdrawn from the cell by means of outlet 178 and analyzed. nd in and o tOf the Cathode Cham r u h that th Based on the analyses, it was foundthat the propylene yg in ng derivative of the propylene feed is oxidewas produced in a selectivity of 61 percent, defined the chlorohydrinwhich is recovered as such. Following as the ratio of total propyleneoxide product to total this procedure, run numbers 1-9 of Table II werecarried organic product expressed in percent. out under the indicatedconditions using a porous graphit- Exam 16 V ic carbon anode in runs1-4, and the above-described P cylindrical porous platinized titaniumanode, designated The electrochemical cell of the type illustrated by asAnode C, in runs 5-9, the propylene being fed to each FIGURE 12 was alsooperated as described in Example anode under the pressure indicated toaid diffusion there- IV except that a dense graphite anode having anaverage of through the porous surface.

TABLE 11 Run Number 1 2 3 4 5 6 7 8 9 Anode Porous carbon Porousplatinized titanium Operating Conditions:

Anode voltage, volts 2. 41 2. 42 2. 77 1. 88 1. 5 1. 5 1. 54 1. 1. 52Current, amperes 2. 3 2. 3 2. 3 2. 3 2. 3 2. 3 2. 3 2. 3 2. 3 Propylenefeed rate, cc./rn 100 89 74 79 77 80 82 84 84 Anodic pressure, mm. Hg.255-344 250-577 340-420 -153 332-360 350-380 385-414 372-390 382-398Duration, mniutes 1 7 240 241 240 240 240 240 240 240 Alnloly Aqueoussodium chloride solution p In 7.7 7.7 9.2 7.9 7.7 9.9 8.3 0.7 12.6 1.00.9 0.8 1.0 1.1 0.9 1.1 0.4 4.2 Feed rate, cc./min 6.5 6.2 6.4 7.4 7.16.6 13.1 6.6 6.7 01- concentration, normality:

In. 1.46 1.47 1.44 1.43 1.50 1.46 1.63 1.48 On 1.42 1.44 1.42 1.45 1.471.49 1.48 1.61 149 Temperature, F 124 124 125 124 124 125 125 125Products, Percent Faradays Basis:

Propylene Chlorohydrin:

10 7; 0 8.1 7. 2 6. 4 8.3 8.7 4. 9 s. 9 0.9 0.9 3.5 1.5 1.1 0.5 1.1 1.20.8 1.1 0.8 3.5 2.9 0.2 0.7 0.7 0.0 0.8 97 96 96 96 101 99 99 83 99.40.3 0.2 0.2 0.8 0.1 0.1 0.1 Percent Conversion -10 23 25 26 29 29 30 2730 Faradie balance (approximate) 94 87 86 89 82 92 87 85 96 Average overindicated duration of runs. 1 Less than 0.001.

porosity of 20 percent was used in place of Anode A. The data of TableII illustrate that by the method of Aqueous solution containing 87 gramsper liter of disthis invention, an impr y d meth d is pr vided for thesolved sodium chloride was fed to the anode compartment manufacture ofhalohydl'lll defiv'fltives 0f Olefins, as Shown at a flow rate of 15 cc.per minute. Propylene was fed to y the f thjat the P l of the F l as theback of the graphite anode at a rate of 614 cc. per heated m parmfularby aflodlqvoltage was slgPlficant' minute. The cell was operated at atemperature of less B1 7 g the Platmlzed mamum anodes m place o grap1t1c car on. 2; gs ggjf i z 23???? sgf s g i 60 In the following TableIII, operating conditions and h r 11 g b 1 ope u 7 i SS results ofanother series of runs are given in which t Ce Pctuated etween an V0 onpropylene was reacted in a cell of the type illustrated by an analyslsof the gaseous efiluent from the CathfJde FIGURE 11 except that the cellwas modified as described Partment and of h yt the p py OXlde p above toallow for recovery of propylene chlorohydrin as not was produced in aselectivity of 55 percent. 5 such from the anode compartment byemploying a solid A comparison f h results b i b Examples 1 barrier ofglass between the opposing anodic and catnodic and V each of which wasoperated at a current density surfaces- In thase -P PY f Was e e y ofamperes per square foot, shows that by )perating t0 the anolytecontaining the lndicated metal chloride, the olefin oxide producing cellusing the platinized ti- 2 3 5 porfms if 156 of glass i tanium anode inplace of carbon, the cell operated with 70 n ense 'grap lte was used asthe anode mmenal' In runs 13-15, the above-described porous platinizedtitanium Anode C was employed as anode 152 and the propylene reactantwas fed directly to the anolyte by means of sparge 156 rather thanthrough the porous surface of the anode.

TABLE III Run Number 11 12 13 14 Anode Carbon Platinized titaniumOperating Conditions:

Anode voltage, volts.. 2. 09 2.04 1.4 1.4 1. Current, amperes 2. 3 2. 32. 3 2. 3 2. 3 Propylene feed rate, cc./m 7 77 90 78 Anodic pressure,mm. Hg 245-673 291-604 243-262 248-252 238-245 Duration, minutes 24 242240 241 240 Afiolyte NaCl KCl NaCl NaCl NaCl p 0. 6 0. 6 9. 4 9. 4 9.10. 4 0. 4 1. 0 1. 0 1. 0 Feed rate, cc./min 7. 6 7. 1 6.6 6. 7 7. 3 01-concentration, normality:

In 1.65 1.52 1.32 1.35 1.44 Out 1.65 1.04 1.33 1.37 1.36 Temperature,125 I25 125 125 125 Products, Percent Faradays Bns PropyleneChlorohydrin:

Anolyte 1 68 73 83 81 79 Catholyte.-- Diehloropropane. 9. 8 6. 1 4. 5 4.5 7. 9 CO 2.9 2.8 4.0 4.4 7.7 0 3.6 2.8 0.0 0.0 0.0 11*. 97 99 98 99 101Other 0.2 0. 1 Percent Conversion. 28 28 41 28 24 Faradic balance (app84 92 1 Average over indicated duration of runs. 2 Less than 0.001.

The data of Table III further demonstrate that in operating the cell toproduce and recover halohydrin derivatives of the olefin by feeding theolefin directly to the anolyte through a sparge, a marked reduction inthe power requirement of the cell is also realized by using platinizedtitanium as the reactive anodic surface. This is indicated,

as in the other tabulated data herein, by comparison of 30 propane, areexpressed on flow of anolyte containing propylene chlorhydrin formed inthe anolyte was maintained from the anode compartment through the fluidpermeable diaphragm into the cathode compartment wherein thechlorohydrin was converted to propylene oxide. In Table IV the yields ofthe pricipal products, namely, propylene oxide and dichlorothe basis offaradays.

TABLE IV Run number 16 17 18 19 20 Operating Conditions:

Temperature, F 125 125 125 125 Anode voltage, volts 1. 60 1. 56 1. 55 1.58 1. 61 Current density, amperes/sq. ft 70 70 70 50 70 Propylene flowrate, cc.lmin 330 300 240 400 400 Aqueous medium:

Electrolyte NaOl NaCl NaCl K01 K01 Concentration, normal 1. 36 1. 48 1.52 0. 70 0. 68 Flow rate, co./m1n 35 35 36 3B 36 pH in 10. 3 10.0 8 10.810. 8 pHout. 12.8 12.4 12.4 12.4 12.3 Duration, hours 4 PrincipalProducts, percent Faradays basis:

Propylene Oxide 86. 2 86. 5 76. 7 77. 1 83. 6 Dichloropropaue l0. 6 11.1 10. 7 7. 5 6.6

the half cell or anodic voltages since the latter are not substantiallyaifected by variables which do affect the cell potential such as thetype and characteristics of the diaphragm, the cathode overvoltage andthe contact potentials.

In the following Table IV, operating conditions are given for runs l620in which propylene was converted to propylene oxide within theelectrochemical cell. In runs 16 and 17, a cell of the type illustratedby FIGURE 12 was employed in which anode 172 was Anode B described aboveunder Example II, and diaphragm 171 in association with cathodic screen169 was liquid permeable white Woven asbestos, the propylene being fedto chamber 182 and diffusing through the pores of the anodic surface.The operation of runs 18-20 was carried out in a cell of the typeillustrated by FIGURE 11 with introduction of the propylene reactant tothe anolyte through sparge 156 In run 18, anode 152 was formed ofcommercially pure non porous titanium having a thickness of 63 mils anda platinum layer electroplated thereon in a thickness of 80micro-inches, diaphragm 151 was formed of liquid permeable polypropyleneand sparge 156 was formed of polyethylene. In runs 19 and 20, anode 152.was formed of a core of non porous titanium having a coating thereon ofplatinum-iridium alloy (7O and 30 weight percent of platinum andiridium, respectively), the coating having a thickness of 1 micron andbeing of the low surface area type. In run 19, the diaphragm and thesparge were each formed of polyethylene. In run 20, White asbestos paperwas used as the diaphragm and the sparge was formed of porous titanium.These runs were conducted such that the Run 21 of the following Table Villustrates still another advantage of the method of this invention. Therun was carried out in a cell of the type illustrated by FIG- URE ll,employing a solid platinized titanium anode 152 having a platinumcoating thereon of the high surface area type and having a thickness of75 micro-inches. Sparge 156 was formed of polyethylene by means of whichpropylene was fed directly to the anolyte. Fluid permeable diaphragm 151was formed of woven, white asbestos, and the flow of aqueous mediumcontaining potassium chloride was maintained from anode compartment 163through the diaphragm into the cathode compartment 164 such that thepropylene chlorohydrin formed in the anolyte was dehydrochlorinated inthe catholyte to form propylene oxide. Aqueous efiluent containing theoxide was withdrawn by means of outlet 161 and then passed through astripping zone operated under the temperature and pressure conditionsgiven in Table V to recover propylene oxide. The aqueous medium was thenpassed through an activated charcoal filter bed (2 cm. thick and 18.5cm. in diameter), and recycled to the anode compartment 163. In thefollowing Table V, run periods I, 2 and 3 correspond to those periodsduring which product was collected and analyzed, the length of each ofsuch periods being designated as the balance period each of which wasbegun after the indicated total number of hours of on stream operationof the cell. For example, run period 2 was begun after the cell had beenon operation for 25 hours and the duration of 2 was 4 hours during which82.6 percent propylene oxide was produced on the basis of faradays.

TABLE V Run Number 21 Run period 1 2 3 Operating Conditions:

Temperature, F 125 125 125 Cell voltage, volts. 3. 31 3. 35 3. 42 Anodevoltage, volts 1. 54 1. 56 1. 60 Current intensity, amperes. 10.8 10. 810.8 Propylene flow rate, ec./min 410 410 410 Aqueous medium:

Electrolyte KC'l KOl KCl Concentration, normality 1. 22 1. o 1 Flowrate, cc./min 33 33 33 pH in 10 10.2 10.2 pH out 12. S 12. 7 12. 6Duration.

Total hours on stream 1 25 49 Balance period, hours 3. 8 4 4. 3 Recyclerate, No. cycles/day 16 16 16 Stripper temperature, C. 32 32 32 Stripperpressure, mm. Hg 34 34 33 Principal Products, Percent Faradays basis:

Propylene oxide 81. 7 82. 6 81. Dichloropropane 9. 1 10. 8 Totalhydrogen eflficiency 90 97 The results of Table V show that during therecycle operation, the voltage and yield of propylene oxide remainedsubstantially constant which are further advantages realized inemploying the electrodes of this invention.

In a specific illustration of operation of the cell of FIGURE 5 of theaccompanying drawings, anode unit 5 is fitted with twenty-nine anodes 2each of which has inner chamber 11 enclosed by side walls 12 which havea thickness of 0.375 inches and are formed of porous platinized titaniumprepared as described above for Electrode A, and by top member 13 whichis formed of solid titanium. Base 14 of each of anodes 2 is also formedof solid titanium and is secured within the slots of currentdistributing plate 35 which is made of electrolytic grade copper, and ofanodizable layer 36 which is formed of titanium. Cathodic unit ismounted on unit 5 such that anodes 2 are in alternating spacedrelationship to tubular cathodes 80 of which there are twenty-eight, theouter surfaces of each of the end anodes being opposed by half-cathodes79. The foraminous surfaces of tubular cathodes 80, the peripheralforaminous wall of the inner cell chamber including vertical side walls82 and 191 and the upper and lower enclosures of peripheral cathodecompartment 92 including upper sections 96 and 97 and lower sections 98and 99 are formed of a screen (wire steel cloth). A diaphragm 103 ofasbestos fiber is deposited on the outer surfaces of cathode tubes 80,on the inner surfaces of side walls 82 and half-cathodes 79, and on theupper and lower surfaces, respectively, of the upper and lowerforaminous enclosures of the peripheral cathode compartment 92. The gapbetween the outer surfaces of anodes 2 and cathodes 80 is approximately0.25 inch, the gap between the outer sides of the end anodes and halfcathodes 79 being about 0.375 inches. Brine containing 8.5 weightpercent of dissolved sodium chloride in water and having a pH of 11 ischarged to inlets 112 within dome 109 at a rate of about 2400 galloonsper hour. The brine flows downwardly by gravity until the desired levelwithin the inner cell chamber is reached which level is observed bymeans of a brine level indicator scale on a manometer (not shown) whichis external to the cell and in fluid communication with the brine withinthe inner cell chamber. The brine level is maintained above the toplevel of anodes 2. The aqueous medium as charged to the cell is at atemperature of about 100 F., and the temperature of the aqueous mediumas it exits from the cell through outlet 118 is about 125 F., theincrease in temperature being caused mainly by the potential drop acrossthe cell. The cell is operated at a substantially atmospheric pressure.A refinery stream of propylene rich gas containing propylene andpropane. is used as the olefinic feed and is charged to olefin inlet 31at a rate of 4.15 pound-moles per hour. The gaseous reactant isintroduced at a slight back pressure of about 5-6 pounds per square inchgauge to obtain uniform difiusion through the pores of side wall 12 ofanodes 2. A source of direct current is supplied to the anode terminalsand cathode terminals at an intensity of 54,000 amperes. The celltherefore is operating at a current density of 100 amperes per squarefoot of apparent electrode surface. The resulting potential drop acrossthe cell terminals is 3.6 volts. Propylene chlorohydrin is produced inthe anolyte which is at an acid pH and is circulated to cathodecompartments within cathodes 80, and peripheral cathode compartment 92,by the direction of flow of the aqueous medium, passing through thediaphragm on the cathodic forarninous surfaces. The propylenechlorohydrin reacts in the cathode vicinity which is at an alkaline pHto form propylene oxide. The acidity of the anolyte and the alkalinityof the catholyte are maintained by having the diaphragm between theanode and cathode compartments. Under these conditions of operation,dichloropropane also is formed in the anode compartment. The anode gasescomprising dichloropropane, unreacted propylene, propane and watervapor, pass upwardly into the free space above the level of the anolyteand exit from the cell by means of outlet 114 within dome 109, thedichloroprop-ane and propylene exiting at a rate of about 0.201 and0.109 pound-moles per hour, respectively. In addition to propyleneoxide, hydrogen gas is also generated within the cathode compartment andis substantially prevented from passing into the gaseous anode cffiuentstream by the diaphragm on the foraminous cathodic surfaces. The cathodegas etlluent containing volatilized propylene oxide and hydrogen arerapidly discharged from the foraminous cathode surfaces by thepassageways provided by apertures 94 in perforated wall 93 and exit fromperipheral'compartment 91. Hydrogen and volatilized propylene oxideproduct pass from compartment 91 at a rate of about 2.21 and 0.403pound-moles per hour, respectively. The aqueous electrolyte medium isdischarged from peripheral compartment 91 by means of outlet 118. Therate of flow of the propylene oxide contained in the brine solution asit exits from the cell on a pound per hour basis, is about 92.5. Aftertreatment to separate dissolved propylene oxide, the brine is furthertreated as required to remove any sludge, adjust the pH, etc., and isrecycled to the cell. On the basis of current input, the faradic balanceis 89.3 percent propylene oxide, 8.0 percent dichloropropane, theremainder being 0.7, 0.5, 0.5 and 1.0 percent, respectively, ofpropylene glycol, oxygen, carbon dioxide and high boilers. Under theabove conditions, the product output of the cell is about 2780 pounds ofpropylene oxide per day. On the other hand, a cell having the same floorarea but equipped with graphitic anodes in place of the platinizedtitanium anodes has a significantly lower product output. For example,when such a cell is operated at the same current density of amperes persquare foot, the maximum total amperage is 31,000 amperes and the outputof propylene oxide is about 1610 pounds per day which is approximately55 percent less than the daily propylene oxide output of the cellequipped with the platinized titanium anodes.

Although the above examples are specific to the use of propylene as theolefin reactant, it is to be understood that other olefins includingthose which are normally gaseous, liquid or solid may be employed. Whensolid, the olefin is charged to the vicinity of the anode dissolved ordispersed in any suitable liquid solvent such as a paraffinic aromatichydrocarbon or mixtures thereof including petroleum fractions such ashydrogenated kerosene, etc. Suitabletypcs of olefins which may be usedare: the alkenes of the homologous series C H wherein n is an integerfrom 2 to about 12 such as ethylene, propylene, butene, pentene, hexene,he'ptene dodecene, etc.; olefins in which the double bond is in anon-terminal position such as Z-butene, Z-pentene, etc.; branchedolcfins such as isobutene isopentene, 4-ethyl-2-hexene, as well asbranched compounds in which the double bond is in 25 the side chain suchas Z-methenepentane and alkenyl compounds; and cyclic olefins such ascyclopentene, cyclohexene, etc. Polyolefins are also useful as feed tothe vicinity of the anode and include those containing isolated,cumulative or conjugated double bonds such as diallyl, allene,butadiene, isopren and 2,3-dimethyl'butadiene. In addition to the above,olefins substituted with aryl and halogen groups also may be used,typical examples of which are styrene, stilbene and allyl chloride.

In addition to sodium and potassium chlorides, the metal halideelectrolyte may be any other water soluble compound whose correspondinghydroxide is also Water soluble. Usually employed are the metal halidesof the alkali metals including sodium, potassium and lithium halides,although alkaline earth metal halides are suitable as well as mixedelectrolytes. The chlorides are usually employed because of theirgreater availability. However, in other instances the choice of halidewill be governed by the ultimate use of the dihalo derivative of theolefin which is formed in varying quantities at the anode. Thus, when itis desired to recover the dihalo by-product as the dichloro compound,metal chloride is used; when the dibromo derivative is desired, a metalbromid is used, etc. When the method of this invention is carried out soas to recover the halohydrin derivative of the olefin as the halohydrin,in place of the metal halide the aqueous medium may contain a hydrogenhalide as the electrolyte such as hydrochloric acid, in which event thehalohydrin may be converted to the oxide in a step external to theelectrochemical cell, as desired.

Various other modifications of the method and appa ratus of thisinvention may become apparent to those skilled in the art from theteachings of this invention without departing from the scope thereof.

What is claimed is:

1. An improved method for converting an olefinic compound to anoxygen-containing derivative in an electrochemical cell which comprisessubjecting an aqueous medium comprising a halide electrolyte andcontained in an electrochemical cell to an electrolyzing current,reacting an olefinic compound in the aqueous medium in the vicinity ofthe anode of said cell, said anode comprising an outer layer of at leastone platinum group metal on a substrate metal formed of at least one ofthe group consisting of titanium, tantalum, zirconium and niobium, toproduce the corresponding halohydrin derivative of the olefin in theaqueous medium in the vicinity of the anode.

2. An improved method for converting an olefin to a chlorohydrinderivative thereof which comprises subjecting an aqueous medium havingan alkali metal chloride dissolved therein and contained in anelectrochemical cell to an electrolyzing current, said cell having ananode compartment and a cathode compartment separated by a substantiallyliquid impervious diaphragm, the anode of said cell being metallic andformed of platinized-titanium, reacting a normally gaseous olefin in theanolyte within the anode compartment to produce the chlorohydrin of saidolefin in the anolyte, and withdrawing aqueous medium from the anodecompartment containing said chlorohydrin.

3. A method for the manufacture of an oxide derivative of an olefiniccompound within an electrochemical cell which comprises subjecting anaqueous medium contained in an electrochemical cell and having a metalhalide dissolved therein to an electrolyzing current, reacting anolefinic compound in the aqueous medium in the vicinity of the anode ofsaid cell to produce the corresponding halohydrin derivative of theolefin in the aqueous medium in the vicinity of the anode, said anodecomprising an outer layer of at least one platinum group metal on asubstrate metal formed of at least one of the group consisting oftitanium, tantalum, zirconium and niobium, maintaining the flow ofaqueous medium containing the halohydrin within the cell from the anodictowards the cathodic electrode region of the cell, dehydrohalogenatinghe halohydrin in the aqueous medium in the vicinity of the cathode toproduce the corresponding olefin oxide and withdrawing efiluent from thecell containing olefin oxide product.

4. A method for the manufacture of an oxide derivative of an olefiniccompound within an electrochemical cell which comprises providing anelectrochemical cell having an anode compartment and a cathodecompartment separated by a fluid permeable diaphragm and containing anaqueous medium having an alkali metal chloride dissolved therein,subjecting said aqueous medium to the action of an electrolyzingcurrent, reacting an olefin in the aqueous medium in the anodic regionof the cell to form the corresponding chlorohydrin derivative thereof,the anodic electrode comprising an outer layer of at least one platinumgroup metal on a substrate metal formed of at least one of the groupconsisting of titanium, tantalum, zirconium and niobium, maintaining theflow of aqueous medium within the cell from the anode compartmentthrough the fluid permeable diaphragm into the cathode compartment suchthat aqueous medium containing the chlorohydrin is passed into thecathode compartment, in said cathode compartment dehydrochlorinatingchlorohydrin to the corresponding olefin oxide and withdrawing effiuentfrom said cell containing olefin oxide as the principal oxygencontainingderivative of the olefin.

5. A method for the manufacture of an oxide derivative of an olefiniccompound within an electrochemical cell having an anode compartment anda cathode compartment separated by a fluid permeable diaphragm andcontaining an aqueous medium having an alkali metal chloride dissolvedtherein, subjecting said aqueous medium to the action of anelectrolyzing current, reacting a normally gaseous olefin in the aqueousmedium in the anode region of the cell to form the correspondingchlorohydrin derivative of the olefin, the surface of the anode whichopposes the cathodic electrode comprising a core of titanium and anouter surface of platinum, maintaining the flow of aqueous medium withinthe cell from the anode compartment through the fluid permeablediaphragm into the cathode compartment such that aqueous mediumcontaining the chlorohydrin is passed into the cathode compartment, insaid cathode compartment dehydrochlorinating chlorohydrin to thecorresponding olefin oxide and wthdrawing effiuent from said cellcontaining olefin oxide as the principal oxygen-containing dedrivativeof the olefin.

6. The method of claim 5 in which at least a portion of said surface ofthe anode is porous and the normally gaseous olefin is contacted withanolyte by diffusion of the olefin through the platinized porous surfacethereof.

7. The method of claim 5 in which the core of titanium is non-porous andin which the olefin is fed to the cell such that it is passed directlyinto the anolyte.

8. The method of claim 5 in which the normally gaseous olefin ispropylene and the olefin oxide produced is propylene oxide.

9. The method of claim 5 in which the normally gaseous olefin isethylene and the olefin oxide produced is ethylene oxide.

References Cited UNITED STATES PATENTS 1,253,615 1/1918 McElroy 204-811,308,797 11/1919 McElroy 2048O 1.992,309 2/ 1935 Hultman 204 3,254,0155/1966 Steele 204-290 FOREIGN PATENTS 303,027 10/ 1929 Great Britain.

877,901 9/1961 Great Britain.

896,912 5/1962 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner.

H. M. FLOURNOY, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATEa-OF CORRECTION 4 at iatent No.3,379,627 April 23, 196

Joseph Adrien M. Leduc It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected asshown below:

In the heading to the printed specification, line 10, 14 244 ,991"should read 224,991 Column 1 line 16,

;L' 229,-5l9" should read 299,519 Column 3 line 62 "meals" lghould readmetals 1 {Column 26, line 44, "wthdrawing'v' should read withdrawin 9lines 45 and 46, "dedrivatiyelig should read derivative Signed andsealed this 24th day of February 1970.

(SEAL) Attest:

' WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioer of Patents Attesting Officer

1. AN IMPROVED METHOD FOR CONVERTING AN OLEFINIC COMPOUND TO ANOXYGEN-CONTAINING DERIVATIVE IN AN ELECTROCHEMICAL CELL WHICH COMPRISESSUBJECTING AN AQUEOUS MEDIUM COMPRISING A HALIDE ELECTROLYTE ANDCONTAINED IN AN ELECTROCHEMICAL CELL TO AN ELECTROLYZING CURRENT,REACTING AN OLEFINIC COMPOUND IN THE AQUEOUS MEDIUM IN THE VICINITY OFTHE ANODE OF SAID CELL, SAID ANODE COMPRISING AN OUTER LAYER OF AT LEASTONE PLATINUM GROUP METAL ON A SUBSTRATE METAL FORMED OF AT LEAST ONE OFTHE GROUP CONSISTING OF TITANIUM, TANTALUM, ZIRCONIM AND NIOBIUM, TOPRODUCE THE CORRESPONDING HALOHYDRIN DERIVATIVE OF THE OLEFIN IN THEAQUEOUS MEDIUM IN THE VICINITY OF THE ANODE.